fix: accepting undefined as an id

It allows better usage of createSelector function

.releaserc.yaml

@@ -14,5 +14,11 @@ plugins:
     - - @semantic-release/github
       - assets:
             - tmp/*.tgz
+        successComment: |-
+            ${nextRelease.version} has been released and contains a fix for the issue.
+            Feel free to reopen the issue or to submit a new one if you meet any problems.
+        failTitle: false
+        failComment: false
+        labels: false
     - - @semantic-release/git
       - message: "chore(release): ${nextRelease.version}\n\n${nextRelease.notes}"

README.md

@@ -26,7 +26,9 @@
 * [rootEntities function](#rootentities-function)
 * [relationships pipe operator](#relationships-pipe-operator)
 * [rootEntityFlags options](#rootentityflags-options)
-* [Releasing cache](#releasing-cache)
+- [Releasing cache](#releasing-cache)
+- [Usage with createSelector](#usage-with-createselector)
+- [NGRX integration](#ngrx-store-integration)
 
 ## Problem
 
@@ -473,6 +475,54 @@ store.select(selectUser, 1).subsribe(user => {
 });
 ```
 
+### Usage with createSelector
+
+Imagine there are a selector that returns id of a current user and a selector with relationships:
+```typescript
+export const selectCurrentUserId = createSelector(
+    selectUserFeature,
+    feature => feature.currentUserId,
+);
+
+export const selectUserWithCompany = rootEntity(
+    selectUserFeature,
+    relatedEntity(
+        selectCompanyFeature,
+        'companyId',
+        'company',
+    ),
+);
+```
+
+Then we have 2 options:
+
+* combine them together via `createSelector` function
+* usage of `switchMap`
+
+#### combine them together via `createSelector` function
+
+```typescript
+export const selectCurrentUser = createSelector(
+    s => s, // selecting the whole store
+    selectCurrentUserId, // selecting the id of a current user
+    selectUserWithCompany, // selecting the user with desired relationships
+);
+
+store.select(selectCurrentUser).subscribe(user => {
+    // profit
+});
+```
+
+#### usage of `switchMap`
+
+```typescript
+store.select(selectCurrentUserId).pipe( // selecting the id of a current user
+    switchMap(id => store.select(selectUserWithCompany, id)),  // selecting the user with desired relationships
+).subscribe(user => {
+    // profit
+});
+```
+
 ### Gathering information of a selector
 
 Besides the `release` function every selector provides information about itself.

src/rootEntity.ts

@@ -65,7 +65,7 @@ export function rootEntity<STORE, ENTITY, TRANSFORMED>(
     const cacheLevel = '0';
     const cache: CACHE<STORE> = new Map();
 
-    const callback = (state: STORE, id: ID_TYPES) => {
+    const callback = (state: STORE, id: undefined | ID_TYPES) => {
         if (!id) {
             return;
         }

src/types.ts

@@ -62,12 +62,12 @@ export type ENTITY_SELECTOR<S = any, E = any> = {
 };
 
 export type HANDLER_ROOT_ENTITY<S, E, T, I> = ENTITY_SELECTOR<S, E> & {
-    (state: S, id: I): undefined | T;
+    (state: S, id: undefined | I): undefined | T;
     release(): void;
 };
 
 export type HANDLER_ROOT_ENTITIES<S, E, T, I> = ENTITY_SELECTOR<S, E> & {
-    (state: S, id: Array<I>): Array<T>;
+    (state: S, id: undefined | Array<I>): Array<T>;
     release(): void;
 };